1. Field of the Invention
The present invention relates to the fields of pixel driving technology of the light emitting diode display, and in particular to an array substrate of organic light emitting diode (OLED) display.
2. The Related Arts
Organic Light Emitting Diode (OLED) has features of faster response, higher contrast, wider viewing angle and etc. compared to conventional liquid crystal panel. Hence, OLED has the increasingly widespread attention from the display technology developers.
FIG. 1 shows an active array OLED driving circuit of 2T1C according to the existing technology. Wherein, 2T1C indicates that the circuit comprises 2 TFT transistors and one capacitance (C). Wherein, the TFT1 is a switching thin film transistor, which is mainly used to control the on/off of the charging capacitance, the driving transistor TFT2 is used to drive the OLED, the capacitance C is used to store the gray scale voltage in the data line signal and thus control the driving current of TFT2 to OLED, Gate n is the n-th row of scanning signal lines, Data is the n-th column of data line and Vdd is a OLED driving line. The drain of the traditional driving transistor TFT2 is connected to the GND, which is unidirectional conductive drive, namely DC drive.
OLED emits light by the current generated from the driving transistor under saturated state. At present, OLED is facing a lot of problems, especially is the aging problem of OLED, which is the very common problem, faced by all of the current light-emitting OLED display. Due to most of the existing technology using DC drive technology, the transmission direction of holes and electrons is fixed, which are injected from the anode and cathode to the light emitting layer, respectively. Then, an exciton is formed in the light emitting layer with the radiation of light. The extra holes (or electrons) which are not recombined, or accumulate in the interface of the hole transport layer/light-emitting layer (or light-emitting layer/electron transporting layer), or cross over the barrier and flow into the electrode. With the extension of the usage time of OLED, many uncomplexed carrier will accumulated at the interface of the light emitting layer and form the built-in electric field inside the OLED. This will cause the threshold voltage Vth of the light emitting diodes to be increase continuously and reduced its luminescence brightness and energy efficiency. It does not help to solve the fundamental aging problem of OLED.